1. Field of the Invention
Embodiments of the present invention relate to vehicle seats, specifically to vehicle seats with a headrest.
2. Description of the Related Art
A conventional vehicle seat such as a car seat is equipped with a headrest for supporting the head of an occupant. An interior of the headrest is filled with a pad configured to exert an appropriate elastic force. When, for example, a collision is generated from behind a car (hereinafter such collision from behind will be referred to as “back collision”), the headrest reliably supports the head of the occupant. This helps to secure the safety of the occupant.
There are various kinds of back collisions. For example, as shown in FIGS. 14 to 17, there is a collision in which the occupant is thrown backwards before his body moves upward. As shown in FIGS. 18 to 22, there is a collision in which the occupant is thrown backwards before his body moves downward. Further, there is a collision in which the body moves upward before moving downward.
In the case when the body moves upward after the collision, the head of the occupant is supported as long as it is supported by the pad of the headrest. As shown in FIG. 16, however, when the body moves upward, the head receives a backward rotating force. As a result, there is a possibility of the occupant suffering a so-called whiplash injury.
Also in the case when the seat falls down toward the floor after the collision, relative movement between the head and the headrest is typically generated. As a result, there is the possibility that the occupant may suffer a whiplash injury.
In the situation when the body moves downward after the collision, the head of the occupant is supported as long as it is supported by the pad of the headrest. As shown in FIG. 21, however, when the body moves downward, the head receives a forwardly rotating force. As a result, there is the possibility that the occupant may suffer a whiplash injury.
Japanese Laid-Open Patent Publication No. 2008-149862 discloses a vehicle seat headrest having a tension spring and a sensor. When the sensor predicts a back collision, urging force of the tension spring is released by using a solenoid. The tension spring causes the movable headrest to move upward. The headrest is forcibly moved upward not at the point in time when the back collision is generated but at the stage when the back collision is predicted. Thus, when the body of the occupant moves upward, there is a possibility that the timing with which the body moves does not coincide with the timing with which the headrest moves. Accordingly, it may be impossible to sufficiently prevent the backward rotation of the head of the occupant. Even when simultaneous timing is attained, the movement distance of the headrest is fixed. Thus, when the movement distance of the headrest is excessive or insufficient, it may be impossible to sufficiently prevent the backward rotation of the head of the occupant. When the body of the occupant moves downward, the headrest may further increase the force with which the head of the occupant is rotated forward. This phenomenon is undesirable.
Therefore, there is a need in the art for a vehicle seat which helps to reduce a burden on an occupant's neck when a back collision or the like occurs.